Effect of vinyl acetate content on the photovoltaic‐encapsulation performance of ethylene vinyl acetate under accelerated ultra‐violet aging

Abstract

The vinyl acetate (VA) content in ethylene vinyl acetate (EVA) can significantly affect its performance as an encapsulant in photovoltaic modules under field conditions. EVA films of varying VA content (18, 24, 33, and 40%) have been prepared using twin screw extruder with the necessary additives and subsequently cured at 150 C. All the EVA films have been subjected to UV radiation at a wavelength of 340 nm for 1000 and 2000 h to simulate accelerated field aging. The effects of accelerated aging on the gel content, mechanical properties, transmittance, Fourier transform infra-red (FTIR) spectra, thermal stability, degree of crystallinity, and yellowness have been studied. The observations made in this study of UV aging up to 2000 h suggests that the optimum range of VA content in EVA should be between 18 and 33% by weight. VA content beyond 40% degrades almost all properties needed for an encapsulate material after aging of only 2000 h. VA content of around 18% is the most stable under UV aging conditions but has a slightly lower value of transmittance for the unaged sample although the difference in transmittance between different specimens decreases with UV aging.

Self-Healing in Mobility-Restricted Conditions Maintaining Mechanical Robustness: Furan–Maleimide Diels–Alder Cycloadditions in Polymer Networks for Ambient Applications

“…Therefore, overlying layers are required to be highly transparent for ultraviolet and visible light. Preliminary tests on 3M-F375PMA film with a thickness of 0.50 mm show a transmittance of T > 85% between 1000 and 515 nm, and a UV-cutoff at 315 nm ( Figure S5 in the Supplementary Materials), which is comparable to poly(ethylene-co-vinyl acetate) (EVA) used as photovoltaic encapsulants [58].…”

“…Due to mismatching thermal expansion coefficients of the different layers, thermal cycling can lead to thermal stress [59]. Therefore, conventional encapsulant layers, such as EVA and polyolefin elastomer (POE) [58], are susceptible to the formation of micro-defects, which may impair solar panel efficiency if they grow into larger defects. Introducing self-healing properties into the encapsulant material can help prevent crack growth in the encapsulant layer through regular healing of newly formed micro-defects.…”

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

“…Copolymers of ethylene and vinyl acetate (EVA) are popularly used as encapsulants in solar PV modules. Accelerated weathering studies on several different EVA copolymers found those with 18–33% by weight in copolymer vinyl acetate to be the most stable to solar UV radiation [ 481 ]. The encapsulant degradation of EVA by solar UV radiation, as assessed by FTIR, was found to be inhomogeneous, suggesting that intrusion of oxygen and moisture from the edges into the interior of laminates governed their degradation process [ 482 ].…”

Comparison of Degradation Behavior of Newly Developed Encapsulation Materials for Photovoltaic Applications under Different Artificial Ageing Tests

“…The presence of vinyl acetate moieties in EVA induced a different ability of the material to crystallize. Ethylene segments in vinyl acetate moieties have the tendency to form smaller and less perfect crystals, which melt at lower temperatures compared to the polyethylene units [ 18 , 39 , 40 ].…”

“…During the exposure in the test chamber at 60 °C, smaller crystals with thinner lamellae can melt and crystallize again to form more perfect crystals with thicker lamellae, which melt at higher temperatures [ 27 , 37 ]. Additionally, in the last two steps of the UV test, it is possible to notice a shift of the melting temperature visible in the second heating run of the DSC measurement from 66 °C to 68 °C and finally to 86 °C, which is an indicator for the occurrence of deacetylation reaction [ 18 , 39 ]. Signs of chemo-crystallization are noticeable also when looking at the cooling curve of the thermogram ( Figure 8 d) because the crystallization peak is shifted to much higher temperatures and the temperature range in which the crystallization process takes place is enlarged.…”